The present invention relates to an assembly including a so-called tone ring or exciter ring and a magnetic sensor unit. More particularly, the present invention relates to a portion of a vehicle or other mechanical assembly which is adapted to create a signal of varying voltage output when rotated at varying speeds, with such signal being detected by a pickup or sensor unit with which the rotary part is associated.
The tone ring preferably has a large plurality of teeth, vanes or lands separated by spaces or grooves therein or can also be a simple cylinder with strips of magnetic rubber molded into it or otherwise fastened to it. Passing the lands or magnets by a fixed sensor at varying speeds creates a speed-varying signal in the sensor and gives an indication of the rotational speed of the shaft with which the tone ring is associated.
The assembly is primarily intended for vehicles wherein the rotational shaft speed, and particularly variations in the rotational speed of two or more shafts, is sensed for various purposes. These include use in ABS (anti-lock braking systems), differential actuation or control, traction control, all-wheel drive control, vehicle stability and the like. In addition, the invention can be used in other applications, such as sensing the rotational speed of power take-off shafts or other power transmission devices including one or more rotary shafts.
In the past, tone rings have been fitted onto axle shafts or other rotating members by press fitting them into place like a bearing or seal. This method can be cumbersome at best, and impossible at worst. Other methods of incorporating tone rings on rotary mechanisms involved integrating the tone rings with bearings or with the hubs or with the ring gear, with the tone ring being associated with the rotary part. Because the shaft undergoes deflection in use, and for other reasons, these methods are sometimes not satisfactory, especially where the bearing/sensor system is too rigid to accommodate such shaft deflection in use.
Other tone rings or proposals for tone rings involve installing forces that might easily damage the tone ring or sensor. Still others would lack a unitizing feature, wherein means are provided to prevent axial movement of the tone ring beyond certain limits, or where installing a retainer determines the position of the tone ring, at least approximately.
If a tone ring assembly could be provided which was unitized, as a system approach, it would result in simplified assembly. Likewise, if a tone ring could be made that had mating components installable with low force, especially a construction in which, after installation, the tone ring would grip the shaft more tightly than during initial installation, it would be highly desirable. There are some preferred features of construction whereby initially locating the tone ring on the shaft would be made easier, while ultimate gripping of the shaft essentially would not be compromised. In other words, the force needed to install the tone ring over the shaft would, for reasons of geometry or surface texture, initially be minimal.
It would also be desirable to provide a unitizing retainer in the form of a sleeve with radially inner and outer portions to engage and package a radial flange of the tone ring, or the entire tone ring itself and allow only a limited range of axial movement between flanges of the retainer and tone ring or limited movement of the entire tone ring. Also, this unitizing retainer could be made of one piece in stamped steel or formed in a tough plastic such as Delrin.
Accordingly, it is an object of the present invention to provide an improved tone ring element able to generate a voltage output by rotation, preferably either in the form of a sleeve having multiple lands, grooves, teeth or magnets for signaling an associated magnetic sensor or pickup as the tone ring lands or magnets rotate past the sensor. By xe2x80x9ctone ringxe2x80x9d or like words is meant not only a single ring element, but also a plurality of rings, working in concert with sensors connected to or associated with a rotational speed differential computer and feedback mechanism.
Another object of the invention is to provide a tone ring assembly which is separate from the bearing or seal assembly yet which is associated with an axle shaft supported on such bearings.
Yet another object of the invention is to provide a tone ring assembly which is sufficiently flexible and positioned such that it is able to accommodate limited axle shaft deflections in use, and also accommodate a limited amount of end play in such shafts.
Still another object of the invention is to provide a tone ring and retainer which can initially be installed by an ergonomically acceptable force by placing it with an installation tool in place within the axle tube or housing and then sliding the axle shaft through the tone ring with ergonomically desirable forces and just past its functional position in the application to permit an axially inner axle shaft retainer or xe2x80x9cCxe2x80x9d clip to be installed in a groove in the axle shaft. Thereafter, when the axle shaft is moved just slightly axially outwardly, the clip and the tone ring are centered or aligned axially in place.
A further object of the invention is to provide a design of tone ring and retainer which can be positioned so as to be in an area of the shaft which undergoes minimum deflection in use.
A still further object of the invention is to provide a design which is unitized for simple and relatively foolproof assembly.
An additional object of the invention is to provide a tone ring which, while installing easily, will thereafter use the swell of rubber in reaction to assembly and/or subsequent application lubricant to develop a more firm grip on the shaft.
A still further object of the invention is to create a design of tone ring having an interior diameter including an oil passage or largest diameter, a diameter for the ribs or splines adapted to swell into contact with the shaft and finally, a small portion with an innermost diameter adapted to initially contact its associated shaft.
Another object of the invention is to provide a design which is compatible with the axle configuration so that there is sufficient axial travel of the axle shaft to enable a retainer or xe2x80x9cCxe2x80x9d clip to be dropped in place over the axially inner end of the axle shaft, and thereafter, enable the axle shaft to be pulled out a few millimeters to seat the clip, thus loading a thermoplastic or thermoset spacer as the tone ring slides slightly out to a xe2x80x9chomexe2x80x9d position on the shaft. This spacer can be eliminated if more axial width for retainers is available. It can also be eliminated if the retainer or toner ring flange is made of thermoset or thermoplastic material.
Yet another object of the invention is to provide a tone ring which lies axially inside the seal and bearing, but is held in position axially by engagement between the opposed flanges of the retainer and the flange of the powdered metal sleeve. It is initially held radially by inner diameter ribs on the tone ring, and thereafter held more firmly in place by lubricant induced swelling of these radial ribs. This may take place in steps or stages, if desired. The powdered metal flange may be eliminated or the powdered metal tone ring/flange combination may become two or more pieces assembled or molded as an alternate design.
Still another object of the invention is to provide substantial axial width of the tone ring teeth so the location of the sensor relative to the tone ring accommodates any variation in the stack-up or end play tolerances in the application.
Another object of the invention is to provide a tone ring that will fit over the smallest machined diameter of an axle shaft, leaving larger respective diameters for accommodating the bearings and the oil seal, respectively and allowing the components to be assembled inside the axle tube.
A further object of the invention is to provide a tone ring assembly which inherently allows a desired or correct assembly sequence with the axle shaft, the seal, the bearing and the tone ring. The tone ring assembly can also be reused after disassembly in the field.
An additional object of the invention is to provide a tone ring assembly which will allow passage of oil along one or two paths through the tone ring.
Another object is to provide a textured surface on some or all of the ribs on the tone ring so that these ribs can, in effect, xe2x80x9choldxe2x80x9d the oil or grease against the shaft, for ease of, or better lubricated, installation.
A still further object is to use various processes, such as electrical discharge machining (EDM) or Chemical Etching to roughen or create a textured surface on the tooling used to make the rubber part, consequently imparting a textured surface on the inside of the ribs or splines in the finished, molded product.
The invention achieves these objects and others which are inherent therein by providing an assembly which includes a rotatable tone or exciter ring able to generate a varying voltage output by rotation relative to a magnetic sensor, and ribs on its inner diameter, which includes an optional radial flange, optionally an abutting spacer with radial oil passage spaces, a retainer having at least one radial flange, one or more oil passage features, with the associated sensor being adapted to pick up a speed varying signal as the lands or magnets on the tone ring sleeve pass by the sensor.
The manner in which these and other objects of the invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the present invention set forth by way of example and shown in the accompanying drawings, in which like reference numerals indicate corresponding parts throughout.